The effects of analgesics and antianxiety drugs on experimental pain in volunteers and chronic pain patients are to be measured by sensory decision theory. The long-term goal is to better understand the nature of pain in man. An important step is to develop an adequate conceptual and physical experimental model which examines the interaction between the sensory and emotional components of pain, and which relates experimetal pain with clinical pain. Drugs to be studied are codeine, diazepam, mepivacine, cocaine and naloxone. For the study of experimental pain, thermal stimuli, continuous electrical-induced pain and ischemic pain induced by tourniquets will be used. Data derived from these models will serve to correlate with "tituration" studies of thermal stimuli superimposed in chronic patients with comparable pain. The aim is to study the relationship of sensory decision indices on both types of pain, and to develop a means of quantifying clinical pain by experimental pain and questionnaries. Futhermore, patients who are about to undergo elective operation will be divided categorically into high anxiety group, such as those to have open-heart surgery, and low anxiety group, such as those to have inguinal hernia repair. Their response to verbal events by questionnaire will be studied to determine discriminability and pain report criterion, and to study the interaction between anxiety and pain report. The experiments are also concerned with the effects of the above mentioned drugs on mood and cognitive function. In addition, the effects of distraction on experimental and clinical pain will be studied by means of sensory decision theory.